A "like" sign at the entrance of Facebook headquarters in Menlo Park, California.

Heather Fluit, a spokeswoman for the Department of Housing and Urban Development, said in a statement that the department was "aware of publishedreports that Facebook's advertising tool may allow users to discriminate in housing advertisements".

Their lawsuit comes around one week after ProPublica reported that Facebook enables advertisers to prevent their ads from being shown to users who belong to certain "ethnic affinity" groups - including people the social networking believes have an ethnic affinity of black, Asian-American and Hispanic. Those laws prohibit companies from publishing housing or job ads that discriminate based on factors including race, religion, sex and national origin.

Responding to the story, Facebook said its policies bar advertisers from using the targeting options for discrimination, harassment, disparagement or predatory advertising practices. "We take prompt enforcement action when we determine that ads violate our policies".

Karen Savage in NY and Victor Onuoha and Suzanne-Juliette Mobley in Louisiana are the plaintiffs in the suit, which accuses Facebook of allowing those posting housing and employment ads to discriminate, in violation of the Fair Housing Act and Title VII of the Civil Rights Act of 1964. "Plaintiffs seek to end only the illegal proscribed uses of these functions", the lawyers wrote in the civil complaint, which was filed last Friday.

When ProPublica purchased an ad from Facebook for an event about affordable housing, it was given the option to exclude based on "ethnic affinities" including African American and Hispanic.

The individuals involved in the lawsuit allege Facebook hasn't done enough to address such ads, stating, "No user can tell whether they are subject to illegal discrimination, because the discrimination occurs with the ads they do not see, As a result, the problem will not be remedied unless Facebook is forced to take additional action".

Facebook's advertising platform has come under fire recently after it emerged that it allowed advertisers to exclude certain races from being targeted in ads.

The complaint cited ProPublica's story and included ProPublica's screenshot of the Facebook ad platform's audience-narrowing options. "The lawsuit is utterly without merit and we will defend ourselves vigorously", Facebook's statement read. "Multicultural marketing is a common practice in the ad industry and helps brands reach audiences with more relevant advertising", a Facebook spokesperson told Digital Trends in an emailed statement. Facebook declined to answer ProPublica's questions about HUD's concerns.

The Civil Rights Act of 1964 also prohibits the "printing or publication of notices or advertisements indicating prohibited preference, limitation, specification or discrimination" in employment recruitment.